CFM, Velocity & Area Calculator
The continuity equation Q = V × A, solved whichever way you need it — for ducts, grilles, louvers and coil faces.
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Inputs
Solve for
Shape
Results
Enter positive values, then select Calculate.
Method and assumptions
- Q (CFM) = V (FPM) × A (ft²). Area is the free internal cross-section; round A = πD²/4.
- For grilles, louvers and diffusers use the manufacturer's free (effective) area, not the nominal face size.
- Rectangular sizes from area are geometric only — for friction-equivalent sizing use the Duct Sizer or Rect ↔ Round converter (Huebscher equivalent diameter).
- Airflow and velocity shown to the nearest whole unit, area to 0.001 ft².
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Important Disclaimer
This calculator is for preliminary design guidance only. Final duct sizing, construction, and installation must be performed by qualified professionals and comply with applicable codes and standards.